Change-speed control system for utility vehicle having stepless change-speed apparatus for speed-changing engine output and transmitting the speed-changed output to traveling unit

ABSTRACT

A change-speed control system is provided for a utility vehicle having a stepless change-speed apparatus for speed-changing an engine output and transmitting the speed-changed output to a traveling unit. The system includes an engine speed governor for adjusting speed of the engine, an accelerator controller and a change-speed control linkage device for providing operative displacements in the stepless change-speed apparatus and the engine speed governor in association with an operation of the accelerator controller. The change-speed control linkage device sets an operation amount for the stepless change-speed apparatus and an operation amount for the engine speed governor in correlation with the operation amount of the accelerator controller, such that an acceleration ratio for the engine speed is greater than an acceleration ratio for the stepless change-speed apparatus until the engine reaches a predetermined speed and also the stepless change-speed apparatus reaches a predetermined speed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a change-speed control system for autility vehicle having a stepless change-speed apparatus forspeed-changing an engine output and transmitting the speed-changedoutput to a traveling unit and also a change-speed control linkagedevice for linking a displacement of an accelerator controller withoperations of an engine speed governor and the stepless change-speedapparatus, so that the stepless change-speed apparatus may be operatedto an acceleration side in association with an operation of the enginespeed governor to the acceleration side.

2. Description of the Related Art

With such change-speed control system as described above, with anoperation of the accelerator operation, both an adjustment of the enginespeed and an adjustment of speed of the stepless change-speed apparatuscan be made. A change-speed control system of this type is known frome.g. the Japanese Patent Application “Kokai” No.: Hei. 5-260827. Withthis known system, if a selector switch SW is set to a road travelingposition, a vehicle speed controlling means C of a controller 15 isactivated and a engine speed detecting sensor 17 detects an engine speedN. Then, an electric-powered cylinder 11 is driven and controlled insuch a manner that an output of a stroke sensor 16 may agree with acharacteristics calculated in advance for achieving a vehicle travelingspeed in proportion with the detected engine speed N, so as to increasethe engine speed. With this, the electric-powered cylinder 11 will beautomatically driven so as to cause the vehicle traveling speed to varyin association with the increase in the engine speed, and the steplesschange-speed apparatus 4 will be operated to the acceleration side.

However, in the case of the above construction in which the change-speedoperation of the stepless change-speed apparatus is effected inoperative connection or linkage with an engine speed adjustingoperation, when the vehicle is started with speed increasing operationof the engine, in association with this, the stepless change-speedapparatus too will be shifted to the acceleration side. Then, if thestepless change-speed apparatus is shifted to the acceleration side byan acceleration ratio equal to or greater than the acceleration ratio ofthe engine speed, when the vehicle starts or travels at a low speed onan inclined or rough terrain, a relatively large driving load will beapplied to the vehicle. So that, due to this driving load, the start ofthe vehicle can be hindered by insufficient engine power or even anengine stop may occur.

SUMMARY OF THE INVENTION

In view of the above-described state of the art, a primary object of theinvention is to provide a change-speed control system capable ofavoiding the above-described trouble at the start or low-speed travelingof the vehicle when the change-speed operations of the engine and thestepless change-speed apparatus are effected in operative connectionwith each other.

For accomplishing the above-noted object, a change-speed control systemaccording to the present invention comprises a change-speed controllinkage device for providing operative displacements in the steplesschange-speed apparatus and the engine speed governor in association withan operation of the accelerator controller, wherein said change-speedcontrol linkage device sets an operation amount for the steplesschange-speed apparatus and an operation amount for the engine speedgovernor in correlation with the operation amount of the acceleratorcontroller, such that an acceleration ratio for the engine speed isgreater than an acceleration ratio for the stepless change-speedapparatus until the engine reaches a predetermined speed and also thestepless change-speed apparatus reaches a predetermined speed.

With this system, when the engine speed governor is shifted to theacceleration side to increase the engine speed in response to anoperation of the accelerator controller, with the function of thechange-speed control linkage device, the stepless change-speed apparatuswill be shifted to the acceleration side in operative linkage with theacceleration in the engine speed. In the course of this, thechange-speed control linkage device functions such that the engine speedmay be increased by an acceleration ratio greater than that in thestepless change-speed apparatus until the engine reaches a predeterminedspeed and also the stepless change-speed apparatus reaches apredetermined speed. According to this function, with appropriatesetting, as the predetermined engine speed or speed condition, of theengine speed or speed condition with consideration to an engine speed orspeed condition used during the start or low-speed traveling of thevehicle, when the vehicle is started with acceleration of the enginespeed or the vehicle travels on a rough terrain with setting the enginespeed low, the engine will be accelerated by a ratio greater than thestepless change-speed apparatus. As a result, even when a relativelylarge driving load is applied, shortage in the engine output will hardlyoccur, and at the same time, the engine speed governor and the steplesschange-speed apparatus may be operated in operative connection with eachother so that both the engine speed and the speed condition of thestepless change-speed apparatus may be increased.

Therefore, according to this change-speed control system, like theconventional construction, when the engine speed is increased inresponse to an operation of the accelerator controller, the steplesschange-speed apparatus too may be speed-changed to the acceleration sidein accordance therewith, thus allowing vehicle travel with easy speedadjustment. And, at the same time, even when a relatively large drivingload is applied, the possibility of shortage in the engine output islow, so that the vehicle may be started smoothly.

The above-described change-speed control linkage device may be anelectric or mechanical or electric-mechanical type device. According toone preferred embodiment, the change-speed control linkage devicecomprises a pivot link mechanism for dividing an operationaldisplacement of the accelerator controller by a predetermined ratiobetween an operational displacement of the stepless change-speedapparatus and an operational displacement of the engine speed governor.Further, according to one specific construction of this pivot linkmechanism, the pivot link mechanism includes a pivot link memberoperatively connected with the accelerator controller, a governor sidelink member slidable by said pivot link member for operating anoperational portion of the engine speed governor, and a change-speedapparatus side link member slidable by said pivot link member foroperating an operational portion of the stepless change-speed apparatus.According to an important aspect of this construction, the governor sidelink member and the change-speed apparatus side link member are operablyconnected with the pivotal link member as a pivot link such that withincrease in the engine speed, an operational efficiency of the governorside link member by the pivot link member may be reduced and at the sametime an operational efficiency of the change-speed apparatus side linkmember by the pivot link member may be increased.

With the above construction, in response to an operation of theaccelerator controller, the pivot link member is pivoted, so that thegovernor side link member is slid by this pivot link member, thereby tooperate the operational portion of the engine speed governor forchanging the engine speed. At the same time, the change-speed apparatusside link member is slid also by the pivot link member, thereby tooperate the operational portion of the stepless change-speed apparatusfor shifting the stepless change-speed apparatus to the accelerationside. In this, with increase in the engine speed, the governor side linkmember is operated with correspondingly reduced operational efficiencyby the pivot link member, whereas the change-speed apparatus side linkmember is operated with correspondingly increased operational efficiencyby the pivot link member. Therefore, the engine speed governor and thestepless change-speed apparatus may be operated in favorable operativeconnection with each other, such that in an operational range where theengine speed is low, thus tending to invite engine power shortage, theengine will be accelerated by a ratio greater than the steplesschange-speed apparatus and also that even if a relatively large drivingload is applied, since the stepless change-speed apparatus is at a lowspeed, engine power shortage will not or will hardly occur. Whereas, inan operational range where the engine speed is high, thus providingstable engine output, the stepless change-speed apparatus will beaccelerated by a ratio greater than the engine. Hence, in this case, theengine speed governor and the stepless change-speed apparatus may beoperated in favorable operative connection, such that the steplesschange-speed apparatus may be speed-changed speedily and by a relativelylarge ratio, without engine power shortage.

Further and other features and advantages of the invention will becomeapparent upon reading the following detailed disclosure of the inventionwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing entirely a utility vehicle having achange-speed control system according to the present invention,

FIG. 2 is a side view showing the entire utility vehicle,

FIG. 3 is a side view of a vehicle chassis,

FIG. 4 is a plan view of a traveling transmission unit,

FIG. 5 is a schematic of the traveling transmission unit,

FIG. 6 is a section view of a stepless change-speed apparatus,

FIG. 7 is a hydraulic circuit diagram of the stepless change-speedapparatus,

FIG. 8 is a side view showing a condition of a change-speed controlsystem when a stepping operation on an accelerator pedal is released,

FIG. 9 is a side view showing a further condition of the change-speedcontrol system when the accelerator pedal is stepped on,

FIG. 10 is an explanatory view illustrating operational efficiencies ofa control cable and a link rod of a pivot link member,

FIG. 11 is an explanatory view showing engine speed and change-speedcharacteristics of the stepless change-speed apparatus, and

FIG. 12 is an explanatory view showing engine speed and change-speedcharacteristics of the stepless change-speed apparatus, relating to afurther embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, FIG. 2 and FIG. 3, a utility vehicle includes avehicle chassis 4 supported on the ground by a pair of left and rightsteerable tired front wheels 1 and a pair of left and right tired rearwheels 2. The chassis 4 mounts, at its front portion and between thefront and rear wheels, an engine 3 for driving the front and rear wheels1, 2. The chassis 4 further mounts, at its front portion, a driver'scabin 7 including a seat 5 and a sunshade 6. The chassis 4 mounts, atits rear portion, a load carrier 8, which is vertically pivotable by adump cylinder 9 about an axis located rearwardly of the carrier 8 andextending transversely of the vehicle body.

The power of the engine 3 is transmitted to the front and rear wheels 1,2 by a traveling transmission unit shown in FIGS. 4 and 5. Moreparticularly, an output from an output shaft 3 a attached with aflywheel 10 located rearwardly of the engine 3 is transmitted via arotational shaft 11 to an input shaft 31 of a hydrostatic type steplesschange-speed apparatus 30. And, the output from an output shaft 32 ofthis stepless change-speed apparatus 30 is transmitted via a rotationalshaft 12 to a gear transmission 13. Then, the output of this geartransmission 13 is inputted to a rear-wheel differential mechanism 14,and outputs from left and right output shafts 14 a of this rear-wheeldifferential mechanism 14 are transmitted via a rotational shaft 16 tothe rear wheels 2. The front-wheel output from the gear transmission 13is inputted via a clutch mechanism 17 for allowing or breaking powertransmission to the front wheels 1 and rotational shafts 18, 19 to afront-wheel differential mechanism 20. And, left and right outputs fromthis front-wheel differential mechanism 20 are transmitted via arotational shaft 21 to the front wheels 1.

The gear transmission 13, the rear-wheel differential mechanism 14, theclutch mechanism 17 and the rotational shafts 11, 12 are allaccommodated within a transmission casing 25 connected via a flywheelcasing 25 a to the rear of the engine 3. The rear-wheel differentialmechanism 14 is arranged at a more rear side of the vehicle body thanthe gear transmission 13.

With a shifting operation of a shift gear 13 a, the gear transmission 13selectively provides a forward traveling condition in which the outputfrom the stepless change-speed apparatus 30 is switched over to theforward traveling side and a rear traveling condition in which theoutput from the stepless change-speed apparatus 30 is switched over tothe rear traveling side. Further, with a shifting operation of a shiftgear 13 b, the forward driving power is speed-changed to either a highspeed or a low speed and outputted as such.

As shown in FIG. 4 and FIG. 5, the stepless change-speed apparatus 30 isdisposed vehicle-wise rearwardly of the gear transmission 13 of thetransmission casing 25 and also vehicle-wise rearwardly of the left andright output shafts 14 a of the rear-wheel differential mechanism 14.

As shown in FIG. 6, the stepless change-speed apparatus 30 includes ahousing 34 having a port block 33 connected to the rear end of thetransmission casing 25, an axial-plunger type variable displacementhydraulic pump 35 and an axial-plunger type fixed displacement hydraulicmotor 36 housed in the housing 34 at a portion thereof vehicle-wiserearwardly of the port block 33, and an axial-plunger type variabledisplacement hydraulic motor 37 housed in the housing 34 at a portionthereof vehicle-wise rearwardly of the port block 33.

The output shaft 32 of the stepless change-speed apparatus 30 acts as acommon output shaft shared by the two hydraulic motors 36, 37. Inresponse to a change in a swash-plate angle of the variable displacementhydraulic motor 37 by a motor switchover cylinder 38 provided at a rearportion of the housing 34, this hydraulic motor 37 is adjusted to adriving condition or a neutral condition. As may be apparent from FIG. 6and FIG. 7, the port block 33 includes a drive oil passage 39 so thatpressure oil from the hydraulic pump 35 is supplied to the two hydraulicmotors 36, 37 for driving these motors 36, 37. The motor switchover oradjusting cylinder 38 is activated in response to a pilot pressuredeveloped in the driving oil passage 39 when the oil pressure of thispassage 39 exceeds a predetermined oil pressure, thereby toautomatically switch over the hydraulic motor 37 to the drivingcondition. Whereas, when the oil pressure in the driving oil passage 39is below the predetermined oil pressure, the cylinder 38 automaticallyswitches over the hydraulic motor 37 to the neutral condition.

With the above, with this stepless change-speed apparatus 30, as thedriving force transmitted via the rotational shaft 11 from the engine 3is inputted to the input shaft 31 acting as the input shaft for thehydraulic pump 35, this hydraulic pump 35 is driven, so that thehydraulic motors 36 and 37 are driven by the pressure oil from thehydraulic pump 35 and the output shaft 32 is then driven by thesehydraulic motors 35, 37. That is to say, this stepless change-speedapparatus is constructed as an HST capable of transmitting the driveforce from the engine 3 with stepless speed change thereof by changingthe swash-plate angle of the hydraulic pump 35. Further, when the frontand rear wheel driving load in the output shaft 32 is below apredetermined load, the oil pressure in the driving oil passage 39 willbe blow the predetermined oil pressure, so that the motor switchovercylinder 38 switches over the hydraulic motor 39 to the neutralcondition. Accordingly, the pressure oil from the hydraulic pump 35 issupplied only to the fixed displacement type hydraulic motor 36 of thetwo hydraulic motors 36, 37, and only this hydraulic motor 36 is drivenat a high speed. On the other had, when the front-rear driving load inthe output shaft 32 exceeds the predetermined oil pressure, the oilpressure in the driving oil passage 39 will exceed the predetermined oilpressure, so that the motor switchover cylinder 38 switches over thehydraulic motor 37 to the driving condition. Hence, the pressure oilfrom the hydraulic pump 35 is supplied in distribution to the twohydraulic motors 36, 37, so that the these two hydraulic motors 36, 37are driven at low speed.

As shown in FIG. 6, by simultaneous casting with the transmission casing25, the housing 34 of the stepless change-speed apparatus 30 is formedintegral with the rear of a portion 25 b of this transmission casing 25accommodating the rear-wheel differential mechanism 14 therein. Further,this housing 34 includes a first housing body 34 a accommodating thehydraulic pump 35 and the fixed displacement hydraulic motor 36, theport block 33 detachably screw-connected to the first housing body 34 afor closing a vehicle-wise rear opening of this housing body 34 a, and asecond housing body 34 b bolt-connected to a vehicle-wise rear side faceof the port block 33 and accommodating the variable displacementhydraulic motor 37 and the motor switchover cylinder 38.

FIG. 8 shows a construction of the change-speed control system, in whichan engine speed governor 50 is provided at a side rearwardly of theengine 3 for variably adjusting engine speed through adjustment ofsupply amount of fuel to the engine, and the engine speed governor 50and the stepless change-speed apparatus 30 are operated by means of asingle accelerator pedal 55 provided in the driver's cabin 7.

This change-speed control system includes the accelerator pedal 55connected via its arm portion 55 a to a support shaft 56, a change-speedcontrol linkage device 60 for linking this accelerator pedal 55 to apivotable speed governor portion 51 of the engine speed governor 50 andto a pivotable change-speed controlling portion 40 of the steplesschange-speed apparatus 30, and an automatic return mechanism 70 having areturn spring 71.

With a progressive stepping-on operation of the accelerator pedal 55,depending on this stepped-on operational amount, as shown in FIG. 9, thearm portion 55 a is pivoted downward about an axis of the support shaft56 extending transversely relative to the vehicle body, and this armportion 55 a can be pivoted to a stepped-on limit position where itcontacts a stopper formed by a cable holder 57. With release of thestepping-on operation, the arm portion 55 a is pivoted upward about theaxis of the support shaft 56 by the operational force of the returnspring 71 to be automatically returned to a stepped-on released positionshown in FIG. 8.

Next, the construction of the change-speed control linkage device 60will be described. First, a link pivot member 63 as a pivot linkpivotally connected to a support shaft 68 included in the transmissioncasing 25 via an attaching boss 63 a located between a connector pin 65to which a governor side control cable 64 is connected and a connectorpin 62 to which a joint 66 connected to a link rod 67 and an apparatusside control cable 61 are connected. So that, the link pivot member 63can be pivoted about the axis 68 a of the support shaft 68, relative tothe transmission casing 25.

To an output arm portion 55 b extending from the base of the arm portion55 a of the accelerator pedal 55, one end of an inner cable 61 a of acontrol cable 61 is connected. And, an end of an outer cable of thecontrol cable 61 is supported to the cable holder 57.

The other end of the inner cable 61 a of this pedal side control cable61 is pivotally connected via the connector pin 62 to one free end ofthe pivot link member 63. An end of an inner cable 64 a is pivotallyconnected via the connector pin 65 to the other free end of the pivotlink member 63. The other end of the inner cable 64 a is connected tothe speed governor portion 51. The pivot link member 63 and the speedgovernor portion 51 are operatively connected via a governor sidecontrol cable 64. To a free end of the pivot link member 63 to which thepedal side control cable 61 is connected, one end of the link rod 67 isconnected via a joint 66. And, the other end of this link rod 67 isconnected to the change-speed controlling portion 40 by the joint 66.

Both the joint 66 connecting the link rod 67 to the pivot link member 63and the joint 66 connecting the rod to the change-speed controllingportion 40 comprise joints screw-connected to the link rod 67. And, thisjoint has a spherical joint portion. Then, by utilizing this sphericaljoint portion, the joint is pivotally connected to the pivot link member63 or the change-speed controlling portion 40. Incidentally, one side ofthis spherical joint is screw-connected to the pivot link member 63 orthe change-speed controlling portion 40 via a screw shaft member 66 a.

The linkage design of the pivot link member 63, the governor sidecontrol cable 64 and the link rod 6 is illustrated in FIG. 8, FIG. 9 andFIG. 10. More particularly, a governor side straight line: AL is formedas a straight line extending through the connector pin 65 as a governorconnecting point connected by the control cable 64 of the pivot linkmember 63 and a pivot axis 68 a of the pivot link member 63. Achange-speed apparatus side straight line: HL is formed as a straightline extending through the screw shaft member 66 a of the joint 66 asthe changes-speed apparatus connecting portion connected by the link rod67 of the pivot link member 63 and the pivot axis 68 a of the pivot linkmember 63. And, these lines, i.e. the governor side straight line AL andthe change-speed apparatus side straight line HL are set to intersecteach other.

Further, the pivot link member 63 has a unit pivot angle (a). And, theinner cable 64 a of the control cable 64 is pulled by a stroke amount(AS) in response to a pivotal movement of the pivot link member 63 bysaid unit pivot angle (a). Then, the ratio between (a) and (AS), i.e.AS/a is used as an operational efficiency of the control cable 64 by thepivot link member 63. Further, the link rod 67 is pulled by a stroke(HS) in response to the pivotal movement of the pivot link member 63 bysaid unit pivot angle (a). Then, the ratio between (a) and (HS), i.e.HS/a is used as an operational efficiency of the link rod 67 by thepivot link member 63. According to this linkage design, the higher thespeed of the engine speed governor 50, i.e. the higher the engine speed,the lower the operational efficiency: As/a and the higher theoperational efficiency: HS/a. Further, when the stepless change-speedapparatus 30 is set to the neutral condition, the operationalefficiency: AS/a becomes maximum, while the other operationalefficiency: HS/a becomes minimum.

As shown in FIG. 8, the automatic return mechanism 70 includes a camfollower 72 attached to the attaching boss 63 a of the pivot link member63 to be pivotable therewith, a cam arm 74 pivotally connected via anattaching boss 74 a at one end thereof to the support shaft 73 includedin the transmission casing 25 and pivotally supported to thetransmission casing 25 to be pivotable about the axis of the supportshaft 73, and the return spring 71 attached between this cam arm 74 anda spring-hook pin 75 fixed to the transmission casing 25. The returnspring 71 pivotally urges the cam arm 74 toward the pivot link member63, so that a cam 76 provided by attaching a roller to an intermediateportion of the cam arm 74 is urged against a cam follower face 72 a ofthe cam follower 72, thereby to pivotally urge the pivot link member 63to a stop position ST shown in FIG. 8.

With the above, according to the automatic return mechanism 70, by meansof the elastic resilient force of the return spring 71, the pivot linkmember 63 is pivotally urged to the stop position ST via the cam 76 andthe cam follower 72. With this, the mechanism 70 provides the pivotalurging function so that the change-speed controlling portion 40 may beautomatically returned to the disengaged position where the steplesschange-speed apparatus 30 is neutral and also the speed governor portion51 may be automatically returned to the idling position. When thestepless change-speed apparatus 30 is set to the neutral condition, thecam 76 enters a recess 72 b of the cam follower face 72 a, whereby thecam 76 and the cam follower 72 are engaged with each other. With this,the change-speed controlling portion 40 is fixed at the disengagedposition, thereby to prevent vibrations or an inadvertent pivotaldisplacement of the change-speed controlling portion 40 due to the oilpressure acting on the swash plate of the hydraulic pump 35.

According to the above-described construction, in response to anoperation on the accelerator pedal 55, the change-speed control linkagedevice 60 operates the engine speed governor 50 and the steplesschange-speed apparatus 30 in manners described next.

Namely, when the accelerator pedal 55 is stepped on, this operationalforce pulls the inner cable 61 a of the control cable 61, thereby topivotally operate the pivot link member 63 to the acceleration side.Then, this pivotal operation of the pivot link member 63 pulls the innercable 64 a of the control cable 64, thereby to pivotally operate thegovernor portion 51 of the engine speed governor 50, so that the enginespeed governor 50 is operated to the acceleration side for increasingthe speed of the engine 3. In the course of this, the pivot link member63 pulls the link rod 67, thereby to pivotally operate the controllingportion 40 of the stepless change-speed apparatus 30, so that thestepless change-speed apparatus 30 is operated to the acceleration sidefor increasing the driving speed of the front and rear wheels 1, 2.Further, with the above-described setting of the operational efficiencyAS/a of the control cable 64 by the pivot link member 63 and theoperational efficiency HS/a of the link rod 67 by the pivot link member63, the engine speed governor 50 and the stepless change-speed apparatus30 are operated in operative correlation with each other such that theoperational stroke of the accelerator pedal 55, the engine speed (thespeed of the governor 50) and the speed condition of the steplesschange-speed apparatus 30 may have correlation as shown in FIGS. 11 and12.

That is, the horizontal axes in FIGS. 11 and 12 represent theoperational stroke of the accelerator pedal 55 and the vertical axesrepresent the engine speed (speed of the governor 50) and the speedcondition of the stepless change-speed apparatus 30. And, a curve ATrepresents the engine speed governing characteristics of how the enginespeed (speed of the governor 50) is varied in response to progressiveoperation of the accelerator pedal 55. A curve HT represents achange-speed characteristics of how the speed condition of the steplesschange-speed apparatus 30 is varied in response to progressive operationof the accelerator pedal 55. Namely, as the accelerator pedal 55 isprogressively stepped on from its stepped-on released position, theengine speed governor 50 and the stepless change-speed apparatus 30 areoperated to the acceleration side in operative connection with eachother, with a rate of the acceleration in the engine speed being greaterthan that in the acceleration of the stepless change-speed apparatus 30until the engine speed rises to reach the predetermined speed N and thespeed of the stepless change-speed apparatus 30 rises to reach thepredetermined speed condition H. After the engine speed reaches thepredetermined speed N and the stepless change-speed apparatus 30 reachesthe predetermined speed condition H, the engine speed governor 50 andthe stepless change-speed apparatus 30 will be operated to theacceleration side with such an operative correlation that theacceleration rate of the stepless change-speed apparatus 30 is greaterthan that of the engine speed.

As the predetermined speed N of the engine 3 and the predetermined speedcondition H of the stepless change-speed apparatus 30, the maximumengine speed used during a start-up of the vehicle or its low-speedtraveling on a rough terrain or a speed or speed condition slightlyhigher than the speed condition of the stepless change-speed apparatus30 is set.

Upon release of the stepping-on of the accelerator pedal 55, the pivotlink member 63 is pivotally returned to the stop position ST by theoperational force of the return spring 71 of the automatic returnmechanism 70 and this pivot link member 63 loosens the inner cable 64 aof the control cable 64 so that the governor portion 51 of the enginespeed governor 50 returned to the idling position by the resilient forceof this speed governor 50, so that the engine speed is returned to theidling condition. In this, the pivot link member 63 pushes the link rod67, thereby to return the change-speed controlling portion 40 of thestepless change-speed apparatus 30 to the disengaged position, so thatthe stepless change-speed apparatus 30 is returned to the neutralcondition.

That is to say, if the accelerator pedal 55 is slightly stepped on tooperate the engine speed governor 50 via the pedal side control cable 61of the change-speed control linkage device 60, the pivot link member 63and the governor side control cable 64, thereby to set the engine 3 to aspeed slightly higher than the idling condition, in operative connectionwith this acceleration operation of the engine 3, the change-speedcontrol linkage device 60 operates, via the link rod 67, the steplesschange-speed apparatus 30 from the neutral condition to a powertransmitting condition, whereby the driving force is transmitted to thefront and rear wheels 1, 2 to cause the vehicle to start or to travel ata low speed. In the course of this, the change-speed control linkagedevice 60 operates the engine speed governor 50 and the steplesschange-speed apparatus 30 with such operative correlation with eachother that the engine speed may be increased at a higher rate than theacceleration of the stepless change-speed apparatus 30. With this, theengine 3 is accelerated at a rate higher than the acceleration in thestepless change-speed apparatus 30. As a result, even if a relativelylarge wheel driving load is applied, since the stepless change-speedapparatus 30 is at a relatively low speed condition, there hardly occursengine power shortage. Hence, the start or low-speed traveling of thevehicle may take place smoothly.

When the accelerator pedal 55 is further stepped on, thereby to operatethe engine speed governor 50 for further acceleration to furtherincrease the speed of the engine 3, thereby to set the engine 3 to astill higher speed, in operative connection with this furtheracceleration operation of the engine 3, the change-speed control linkagedevice 60 operates the stepless change-speed apparatus 30 for furtheracceleration, whereby the high speed driving force is transmitted to thefront and rear wheels 1, 2 to cause the vehicle to travel at a highspeed. In the course of this, the change-speed control linkage device 60operates the engine speed governor 50 and the stepless change-speedapparatus 30 with such operative correlation with each other that thespeed condition of the stepless change-speed apparatus 30 may beaccelerated at a higher rate than the acceleration of the engine 3. As aresult, even if a relatively large wheel driving load is applied, powershortage does not occur due to the high speed revolution of the engine3. And, at the same time, the significant change-speed operation of thestepless change-speed apparatus 30 may be effected speedily.

When the stepping-on operation on the accelerator pedal 55 is released,so that the engine speed governor 50 is operated by the functions of thechange-speed control linkage device 60 and the automatic returnmechanism 70, thereby to reduce the speed of the engine 3 to the idlingcondition, in operative connection with this deceleration of the engine3, the link rod 67 of the change-speed control link device 60 returnsthe change-speed controlling portion 40 of the stepless change-speedapparatus 30 to the disengaged position by the operation force of thereturn spring 71 of the automatic return mechanism 70. With this, thestepless change-speed apparatus 30 is set to the neutral conditionwhereby the power transmission to the front and rear wheels 1, 2 isstopped and the traveling of the vehicle is stopped accordingly.

As shown in FIG. 8, the change-speed controlling portion 40 of thestepless change-speed apparatus 30 is connected to and pivotable with anend of a rotational control shaft 41 a of a servo valve 41 (FIG. 7)provided inside the transmission casing 25, which end projects outwardfrom the transmission casing 25. As shown in FIG. 7, inside thetransmission casing 25, there is provided a hydraulic servo cylinder 44connected via a control oil passage 42 to the servo valve 41 and linkedby a feedback mechanism 43. And, this cylinder 44 is operably coupledwith a swash-plate control portion of the hydraulic pump 35. With thesearrangements, the change-speed operation of the stepless change-speedapparatus 30 by the change-speed controlling portion 40 is madepossible.

More particularly, when the change-speed controlling portion 40 ispivotally operated about the axis of the rotational control shaft 41 a,this rotational control shaft 41 a is rotated to switch over the servovalve 41 to the driving condition. Then, the servo valve 41 supplies thepressure oil from the hydraulic pump 45 via the oil passage 42 to theservo cylinder 44. With this, the servo cylinder 44 is driven to changethe swash-plate angle of the hydraulic pump 35 and the driving speed ofthe hydraulic pump 35 is changed correspondingly to change the speedcondition of the stepless change-speed apparatus 30. In this, theoperation of the servo cylinder 44 is fed back to the servo valve 41 bythe function of the feedback mechanism 43. So, when the steplesschange-speed apparatus 30 reaches a control target speed conditioncorresponding to the operated position of the change-speed controllingportion 40, the servo valve 41 is switched over to the neutralcondition, whereby the stepless change-speed apparatus 30 is maintainedat this control target speed condition.

[Other Embodiments]

The foregoing embodiment employs the mechanical type change-speedcontrol linkage device 60. Instead, an electric type control means maybe employed, in which an engine speed governing actuator for operatingthe governor portion 51 of the engine speed governor 50 and thechange-speed controlling portion 40 of the stepless change-speedcontroller 30 are automatically and respectively operated, based ondetection information from a stroke sensor adapted for sensing anoperated position of the accelerator pedal 55, whereby the engine speedgovernor 50 and the stepless change-speed apparatus 30 are operated inoperative correlation with each other according to the operation of theaccelerator pedal 55. Hence, the mechanical type change-speed controllinkage device 60 and such electric control means are genericallyreferred to herein as the “change-speed control linkage device 60”.

When an electric control means is implemented, as shown in FIG. 11 andFIG. 12, it may be arranged such that the engine speed characteristicsAT showing how the engine speed (speed condition of the engine speedgovernor 50) is varied in accordance with an operation of theaccelerator pedal 55 and the change-speed characteristics HT showing howthe speed condition of the stepless change-speed apparatus 30 is variedin accordance with the operation of the accelerator pedal 55 may beprovided a curve comprising combination of a low-speed side straightline and a high-speed straight line.

In place of the governor side control cable 64, various link memberssuch as a link rod, slidable by the pivot link member 63, may beemployed. Further, in place of the link rod 67, various link memberssuch as a control cable, slidable by the pivot link member 63, may beemployed. Hence, such link members as the control cable 64 and the linkrod are generically referred to herein as the “governor side link member64”. And, such members as the link rod 67 and the control cable aregenerically referred to herein as the “change-speed apparatus side linkmember 67”.

The present invention may be applied to a construction which uses, inplace of the hydrostatic stepless change-speed apparatus 30, other typesof stepless change-speed apparatus using a split pulley and a belt orusing a tapered cone. Therefore, these types of change-speed apparatusesof the hydrostatic, belt or tapered-cone types are generically referredto herein as the “stepless change-speed apparatus 30”.

In place of the accelerator pedal 55, an accelerator lever may be use.Or, the accelerator pedal 55 and the accelerator lever may used incombination also. Hence, these members such as the accelerator pedal 55and the accelerator lever, are generically referred to as the“accelerator controller 55”.

The present invention may be applied to a crawler type utility vehicle,in addition to the above-described type of vehicle using the front andrear wheels 1, 2 for traveling. Hence, all these components includingthe front and rear wheels 1, 2 and the crawler traveling unit arereferred to herein as the “traveling units 1, 2”.

The invention may be embodied in any other way than disclosed in theabove detailed description without departing from the essential spiritthereof defined in the appended claims. All modifications apparent forthose skilled in the art are intended to be encompassed within the scopeof the invention defined by the claims.

1 A change-speed control system for a utility vehicle having a steplesschange-speed apparatus for speed-changing an engine output andtransmitting the speed-changed output to a traveling unit, comprising:an engine speed governor for adjusting speed of the engine; anaccelerator controller; and a change-speed control linkage device forproviding operative displacements in the stepless change-speed apparatusand the engine speed governor in association with an operation of theaccelerator controller; wherein said change-speed control linkage devicesets an operation amount for the stepless change-speed apparatus and anoperation amount for the engine speed governor in correlation with theoperation amount of the accelerator controller, such that anacceleration ratio for the engine speed is greater than an accelerationratio for the stepless change-speed apparatus until the engine reaches apredetermined speed and also the stepless change-speed apparatus reachesa predetermined speed.
 2. The change-speed control system according toclaim 1, wherein the change-speed control linkage device comprises apivot link mechanism for dividing an operational displacement of theaccelerator controller by a predetermined ratio between an operationaldisplacement of the stepless change-speed apparatus and an operationaldisplacement of the engine speed governor.
 3. The change-speed controlsystem according to claim 2, wherein the pivot link mechanism includes apivot link member operatively connected with the accelerator controller,a governor side link member slidable by said pivot link member foroperating an operational portion of the engine speed governor, and achange-speed apparatus side link member slidable by said pivot linkmember for operating an operational portion of the stepless change-speedapparatus.
 4. The change-speed control system according to claim 3,wherein the governor side link member and the change-speed apparatusside link member are operably connected with the pivotal link member asa pivot link such that with increase in the engine speed, an operationalefficiency of the governor side link member by the pivot link member maybe reduced and at the same time an operational efficiency of thechange-speed apparatus side link member by the pivot link member may beincreased.